Qualification of a Surrogate Matrix-Based Absolute Quantification Method for Amyloid-β₄₂ in Human Cerebrospinal Fluid Using 2D UPLC-Tandem Mass Spectrometry

Article type: Research Article

Authors: Korecka, Magdalena^a | Waligorska, Teresa^a | Figurski, Michal^a | Toledo, Jon B.^{a; d} | Arnold, Steven E.^{b; c} | Grossman, Murray^c | Trojanowski, John Q.^{a; d} | Shaw, Leslie M.^{a; d; *}

Affiliations: [a] Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA | [b] Department of Psychiatry, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA | [c] Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA | [d] Institute on Aging and Center for Neurodegenerative Disease Research, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

Correspondence: [*] Correspondence to: Leslie M. Shaw, PhD, Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA. Tel.: +1 215 662 6575; Fax: +1 215 662 7529; E-mail: Les.Shaw@uphs.upenn.edu.

Abstract: The primary aims of this work were to: 1) establish a calibrator surrogate matrix for quantification of amyloid-β (Aβ)42 in human cerebrospinal fluid (CSF) and preparation of quality control samples for LC-MS-MS methodology, 2) validate analytical performance of the assay, and 3) evaluate its diagnostic utility and compare it with the AlzBio3 immunoassay. The analytical methodology was based on a 2D-UPLC-MS-MS platform. Sample pretreatment used 5 M guanidine hydrochloride and extraction on μElution SPE columns as previously described. A column cleaning procedure involved gradual removal of aqueous solvents by acetonitrile assured consistent long-term chromatography performance. Receiver-operator characteristic (ROC) curve and correlation analyses evaluated the diagnostic utility of UPLC-MS-MS compared to AlzBio3 immunoassay for detection of Alzheimer's disease (AD). The surrogate matrix, artificial CSF containing 4 mg/mL of BSA, provides linear and reproducible calibration comparable to human pooled CSF as calibration matrix. Appropriate cleaning of the trapping and analytical columns provided every-day, trouble-free runs. Analyses of CSF Aβ42 showed that UPLC-MS-MS distinguished neuropathologically-diagnosed AD subjects from healthy controls with at least equivalent diagnostic utility to AlzBio3. Comparison of ROC curves for these two assays showed no statistically significant difference (p = 0.2229). Linear regression analysis of Aβ42 concentrations measured by this mass spectrometry-based method compared to the AlzBio3 immunoassay showed significantly higher but highly correlated results. In conclusion, the newly established surrogate matrix for 2D-UPLC-MS-MS measurement of Aβ42 provides selective, reproducible, and accurate results. The documented analytical performance and diagnostic performance for AD versus controls supports consideration as a candidate reference method.

Keywords: Alzheimer's disease, amyloid-β₄₂, cerebrospinal fluid, mass spectrometry

DOI: 10.3233/JAD-132489

Journal: Journal of Alzheimer's Disease, vol. 41, no. 2, pp. 441-451, 2014